1. Field of the Invention
The present invention relates to an oxygen sensor, particularly to an oxygen sensor having a plate-shaped oxygen sensor element.
2. Related Art Statement
Heretofore, in order to improve precision of measurement of an oxygen sensor using a plate-shaped oxygen sensor element, the applicant disclosed in Japanese Utility Model Application Laid-Open No. 60-150,447 an oxygen sensor wherein gas vent holes 23 for ventilating a gas to be measured are positioned on a protective cover 22 protecting a plate-shaped sensor element 21 such that they do not face the surface of the plate-shaped sensor element 21, as shown in the attached FIG. 6(b).
However, in the oxygen sensor of the above Japanese Utility Model Application Laid-Open No. 60-150,447, the measuring electrode 24 is arranged on a broader width surface of the plate-shaped sensor element 21, as shown in the attached FIG. 6(b), so that the oxygen sensor has a drawback in that the gas to be measured impinges differently on the measuring electrode 24 depending on the attached direction of the oxygen sensor. Namely, the gas to be measured impinges in different manners on the measuring electrode 24 of the sensor element 21, depending on the direction A or B of the entrance of the gas in the protective cover 22.
If the manner of impingement of the gas to be measured on the measuring electrode 24 varies just as described above, a measurement of a high precision can not be performed, because the .lambda. controlling point of the oxygen sensor varies and the response at the low flow rate of the gas varies by the reasons described later.